Fuel cells have electrodes arranged on both surfaces of an electrolyte membrane, generate power by an electrochemical reaction of hydrogen and oxygen, and produce only water as a by-product during power generation. Thus, unlike general internal combustion engines, the fuel cell does not produce an environmental load gas such as carbon dioxide, and is therefore expected to spread as a next-generation clean energy system. Above all, polymer electrolyte fuel cells, which are fuel cells using a polymer material for an electrolyte membrane, have a low operation temperature, and are expected to come into practical use early as a home cogeneration system and the like. The basic structure of the polymer electrolyte fuel cell includes a catalyst layer laminated membrane (CCM) produced by laminating catalyst layers to both surfaces of an electrolyte membrane having proton conductivity, and a membrane-electrode assembly (MEA) produced by laminating gas diffusion layers on the catalyst layer laminated membrane, wherein a gasket and a separator are placed on the MEA.
In recent years, the polymer electrolyte fuel cell has had a tendency toward thinning of the electrolyte membrane for power enhancement. As a result, the electrolyte membrane is easily broken, thus contributing to a reduction in durability of the fuel cell. As a method for solving this problem, a technique of reinforcing an electrolyte membrane by adhering a frame-shaped reinforcing material to a produced by laminating gas diffusion layers on the catalyst layer laminated membrane or a membrane-electrode assembly has been proposed (Patent Document 1).
In this catalyst layer laminated membrane or membrane-electrode assembly equipped with a reinforcing material, adhesion of the reinforcing material to the electrolyte membrane and the catalyst layer or the gas diffusion layer in the catalyst layer laminated membrane or the membrane-electrode assembly is performed by interposing an adhesive (adhesive layer) between each adherend and the reinforcing material. However, for example, conventional adhesives are poor in workability in bonding a reinforcing material to an electrolyte membrane, leading to a reduction in productivity. Specifically, since the adhesion force of the adhesive is excessively strong, it is difficult to correct the position of the reinforcing material once the reinforcing material is brought into contact with the electrolyte membrane, and wrinkles and the like generated on the electrolyte membrane during bonding cannot be removed. Conversely, the initial adhesion force of the adhesive is excessively weak, and therefore there is a problem that the reinforcing material is positionally displaced when the reinforcing material is pressure-bonded to the electrolyte membrane.
Accordingly, it has been desired to develop a reinforcing material which can be temporarily fixed to an adherend such as an electrolyte membrane, a catalyst layer and a gas diffusion layer (reinforcing material which allows itself to be adhered with a proper initial adhesion force) in production of a catalyst layer laminated membrane or membrane-electrode assembly equipped with a reinforcing material, and an adhesive that is used for the reinforcing material.